This research will develop standard methods for quantification of physiological sexual functions in human females and males. These will apply objective numerical results to the previously subjective descriptions of the human sexual response. A definition of physical health by objective parameters includes the establishment of time-qualified (daily and monthly rhythmic) normal ranges for sexual variables. Methodological and instrumentational problems encountered in previous published methods for measuring sexual arousal are discussed. Development of a vaginal probe is described which simultaneously measures vasocongestion and increased pubococcygeal muscle tone associated with female genital arousal. Other variables describing general arousal (heart rate and blood pressure) are monitored by conventional methods. Physical responses will be related to significant aspects of past sexual history and current subjective sexual feelings. Available sex history questionnaires are inappropriate as they are primarily oriented toward sex therapy and focus on the dysfunctional aspects of sexual experience. Construction of a sex history is briefly described which emphasizes the positive dimensions of past sexual development and current sex image. In the male studies a mercury strain gauge will be constructed which records slight changes in penile circumference on a portable magnetic tape recorder. It will be used to determine whether the about-90 minute REM-erection rhythm persists during the awake state. About-daily and monthly biological rhythms in tumescence can also be documented. Monthly rhythms in male fertility and sex drive will be determined in a three-month study. The ability to directly compare male and female sexual responses is suggested with the use of a rectal probe which measures changes in vasocongestion and sphincter tone. Applications of the above methods to sexual dysfunction are discussed. Biofeedback training units could utilize the same instrumentation and self-teach pre-orgasmic women and psychogenically impotent men in therapy adjunctive to the conventional counseling methods. A non-chemical and non-mechanical method of contraception is proposed from the male fertility studies.